1) Field of the Invention
The present invention relates to a device for differential-mode information transmission between at least two elements of a motor vehicle, linked by two information transmission lines.
2) Discussion of Related Art
In these devices, each element comprises information sending means and information reception means, linked to a protocol handler.
These differential-mode information transmission devices have been developed during the definition of transmission systems for motor vehicles, because of a certain number of problems linked to these applications and especially parasites which are capable of disturbing these transmissions.
The use of differential transmission makes it possible to obtain a good immunity to these parasites but it exhibits a certain number of drawbacks in the matter of its reliability.
In fact, the latter is linked to the reliability of the connections (microbreaks, oxidation of contacts, etc), to the possibilities for putting one of the transmission wires to the potential of the bodywork or to the battery plus, which has the effect of preventing correct operation of this type of transmission system.
One response to this problem is already known from the document EP-A-0,318,354 in the names of AUTOMOBILES PEUGEOT, AUTOMOBILES CITROEN and REGIE NATIONALE DES USINES RENAULT. In this document, capacitive coupling of the transmission in Polling mode between the various elements of the vehicle is used.
Hence it is possible to make the device described in this document operate according to a normal, differential, or degraded, mode on the basis of the information transiting on one of the information transmission lines.
However, this device is limited to certain applications and is not applicable, for example, to a multi-master information transmission network.
In fact, in a network of this type, all the elements linked to the network can access the transmission lines in order to impose their message on the-latter and it is therefore important to ensure good diffusion of the message and good coherence thereof for all the elements.
The solution proposed in the preceding document cannot resolve the different problems linked to the different defect modes in this type of network.